Conventionally, a joining method of a metal ball has been known in which a metal ball is joined to a joined body formed in a flat plate shape by laser welding (for example, see Japanese Patent Laid-Open No. Sho 61-115691). In the joining method of a metal ball described in the Patent Literature, a circular through-hole having a diameter smaller than that of the metal ball is formed in a joined body and an edge of the through-hole and the metal ball are welded and joined to each other.
In the Patent Literature described above, a method is disclosed in which a metal ball is welded to a surface of a joined body formed in a plate shape. However, in this Patent Literature, a method is not disclosed in which a spherical surface part formed in a spherical surface shape is welded to an end face of a member formed in a plate shape from a side, for example, welded to a side face of a plate spring having a predetermined thickness,.